1. Field of the Invention
The present invention relates to a coated cemented carbide cutting tool, such as a cutting tool insert for the turning of stainless steels, particularly in applications with high demands on the toughness properties of the insert. Additionally, the insert is provided not only for the turning of stainless steels with different compositions and microstructures, such as austenitic, ferritic, ferriteaustenitic, superaustenitic and precipitation hardened stainless steels, but also for the turning of non-stainless steels, such as low carbon steels and low and medium alloyed steels.
2. State of the Art
In the discussion of the state of the art that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicant expressly reserves the right to demonstrate that such structures and/or methods do not qualify as prior art against the present invention.
It is well known that for cemented carbide cutting tools used in the machining of steels, the cutting edge is worn by different wear mechanisms. Examples of such mechanisms include chemical and abrasive wear. Additionally, external variables, such as cutting speed, depth of cut, and cutting feed rate, and external cutting conditions, such as the use of coolant, an off-centered work piece, and a cast skin on a work piece, require a number of different properties of the cutting edge. As an examples, the tool edge may fracture under a heavy intermittent cutting load resulting in so-called edge chipping. The chipping is due to a lack of edge toughness. Furthermore, when turning stainless steel, still another wear mechanism is active called adhesive wear. This type of wear is caused by the adhesive force between the stainless steel chip of the workpiece and the cutting edge. When the adhesive force grows large enough, edge chipping on the cutting edge will occur and, hence, the tool life will be shortened. Also, when utilizing a cemented carbide cutting tool for the turning of a stainless steel part when increasing the cutting speed in a stainless steel grade, the thermal energy developed in the cutting edge is considerable and the entire tool edge may plastically deform. This type of wear mechanism is known as plastic deformation wear and is in clear conflict with the edge toughness required to prevent or minimize edge chipping. Hence, another requirement of the coated cemented carbide insert is that the selection of the carbide composition and the coating material results in a cutting edge exhibiting a high resistance to plastic deformation.
Commercial cemented carbide tools suitable for the machining of stainless steels, such as those described in SE 9602413-8 and SE 9901149-6, are usually optimized with respect to some of the required tool properties mentioned above, i.e. high resistance to mechanical, chemical, abrasive, adhesive, thermal and plastic deformation wear.